Sondes are widely used in horizontal drilling applications such as pipe laying, and utility cable installation applications. In such situations, sondes are used to provide information on the location of the head of the drill. This is generally achieved by emission of an electromagnetic signal from the sonde and detection of the signal on the surface. Additionally, the sonde may provide other information to the surface, such as the azimuthal angle, yaw and pitch etc.
Sondes are generally powered using a wireline from a power supply on the surface to the sonde. Such sondes are generally also controlled from the surface by using a dedicated line within the wireline from the surface, along the pipe, to the sonde. The dedicated line may then also be used for the sonde to communicate back to the surface with details of azimuthal angle etc. Such wireline sondes have a disadvantage that the range is limited by the length of the wireline from the surface to the sonde, and operational time is increased, along with inconvenience and cost, by the need to insert sections of communication and power cable within the rods used to push the drill head and sonde underground during drilling.
Battery powered sondes may be used in order to overcome this range problem. However, removal of the wireline also removes the dedicated control and communication channel meaning that the surface control can no longer directly communicate with the sonde, and the sonde can no longer directly communicate with the surface. In order to overcome this, U.S. patent application Ser. No. 09/504,833, the contents of which are incorporated herein by reference, allows control of the sonde by a series of coded rotations of the head containing the sonde, which the sonde detects and decodes into instructions. The communication from the sonde to the surface can be achieved by applying a modulation to the EM location signal emitted by the sonde. However, such battery powered sondes have disadvantages in that the power of the sonde signal is weakened, resulting in shallower depths of operation than a wireline sonde, both for location of the sonde, and for receiving the further EM modulation of the emissions from the sonde communicating to the surface. Other ambient EM radiation also interferes with the signal reducing the effective range of the sonde.
As discussed above, both wireline and battery powered have advantages and disadvantages. However, a user of sondes is required to buy both a battery powered sonde and a wireline sonde for the different requirements. This is because, generally, it is not possible to combine a battery powered sonde with a wireline sonde in a single apparatus because the circuitry for each is mutually exclusive and a different communication method is used for each, resulting in a size requirement too large to be placed in an industry standard sonde casing.
Therefore, there is a need to provide a single industry standard dimensional sonde that can combine the one or more of the advantages of each type of sonde described above, and/or mitigate or ameliorate at least one of the disadvantages of the prior art.